Experimental measurement of the van der Waals binding energy of X–O₂ clusters (X = Xe, CH₃I, C₃H₆, C₆H₁₂)

Van der Waals binding energies for the X–O₂ complexes (X=Xe, CH₃I, C₃H₆, C₆H₁₂) are determined by analysis of experimental velocity map imaging data for O(³P₂) atoms arising from UV-photodissociation of the complex [A. V. Baklanov et al., J. Chem. Phys. 126, 124316 (2007)]. Several dissociation pathways have been observed, we focus on the channel corresponding to prompt dissociation of X–O₂ into X+2O(³P) fragments, which is present for complexes of O₂ with all partners X. Our method is based on analysis of the kinetic energy of all three photofragments, where the O atom kinetic energy was directly measured in the experiment and the kinetic energy of the X partner was calculated using momentum conservation, along with the measured angular anisotropy for O atom recoil. We exploit the fact that the clusters are all T-shaped or nearly T-shaped, which we also confirm by ab initio calculations, along with knowledge of the transition dipole governing radiative absorption by the complex. The effect of partitioning the kinetic energy between translation along the X–O₂ and O$-$O coordinates on the angular anisotropy of the O atom recoil direction is discussed. Van der Waals binding energies of 110 ± 20 cm⁻¹, 280 ± 20 cm⁻¹, 135 ± 30 cm⁻¹, and 585 ± 20 cm⁻¹ are determined for Xe$-$O₂, CH3I$-$O₂, C₃H₆$-$O₂, and C₆H₁₂$-$O₂ clusters, respectively.